1. Field of the Invention
The present invention relates to a television telephone apparatus.
2. Description of the Related Art
According to the recent development of highly information-oriented society, there is an increasing demand for communication media by which a vast amount of various types of information are transmitted fast. To fulfill such a demand in Japan, the "analog telephone band still picture video communication system" was established in 1988 as a standard communication system to allow for communication of a monochromatic image between parties over a communication line. The standards was amended in 1989 so that a color image as well as a monochromatic image can be exchanged. Various television (TV) telephone apparatuses which conform to those standards have been developed so far. The TV telephone apparatuses are expected to become popular because of their advantages that visual information can be sent to cover voice-based information or explanation which is often difficult to consume or visualize and that telephone communication is possible while watching the caller's or receiver's expressions.
TV telephone apparatuses are classified by types of communication networks to be linked and the types of image and voice transmission functions. For example, some TV telephone apparatuses are connected to an analog public telephone line to transmit a monochromatic still picture or a color still picture, or to transmit a color dynamic image. The still-picture TV telephone apparatus, which is connected to an analog public telephone line to send a monochromatic still picture, employs a system for directly transmitting image data without compression. For monochromatic image data of 64 gray scales (6 bits) with one screen consisting of 100.times.160 pixels, for example, data of about 100.times.160.times.6=96000 bits (about 11.7 Kbytes) has been transmitted at a transfer rate of about 8740 bps (bit per second). This takes about 11 seconds to send one screen of image data.
Image data carries a large amount of information so that direct processing of image data is not practical in view of memory capacity, communication speed and so forth. As a solution, there has been proposed a color dynamic-image TV telephone apparatus which compresses image data and voice data to about 1/20 to 1/100before transmission to thereby ensure transmission and reception of a dynamic image at a rate of two to ten frames per second using an analog telephone band.
As the compressed transmission of image data will transfer a considerable amount of data, a slight transmission delay will not affect the progression of telephone communication so much. Therefore, variable length coding (e.g., variable length coding system which conforms to H. 261 of the CCITT (Comite Consultatif International Telegraphique et Telephonique) regulations) is typically employed.
In compressed transmission of voice data, digitalization of voice data can compress the length of the average produced bits. Generally speaking, if entropy compression (e.g., Hoffman coding) which does not guarantee the maximum bit length is adapted for voice signals, a large transmission delay of voice signals occurs when voice signals are converted to a long bit length by the entropy compression. This would greatly affect the progression of telephone communication. In this respect, voice data is encoded with a fixed bit length before transmission.
TV telephone apparatuses, which are connected to such an analog communication network, have a communication function to transmit/receive image data and voice data in multiplexed form. A communication protocol corresponding to the communication networks to be linked and a coding system for image data and voice data, which are affixed to a protocol-based communication signal for transmission/reception, are specified for each type of communication network by the CCITT regulations, etc.
The conventional TV telephone apparatuses generally have an integrated telephone function and therefore become inevitably large.
Liquid crystal (LC) televisions recently become popular and are installed on vehicles or used to watch TV programs, such as sport programs. Pocket-size LC televisions have been developed so that users can watch TV programs any time on their ways to offices or on business trips.
Telephones are often used outside offices, but they of course permit only voice communication.
In the conventional TV telephone apparatus which compresses image data and voice data before transmission, a camera as an image input/output unit, a CRT (Cathode Ray Tube) as an image display unit, and a telephone as a voice input/output unit are designed as one integrated unit to transmit compressed data. It is therefore difficult to provide compact and light portable TV telephone apparatuses. Further, the existing telephones cannot be used in such a TV telephone apparatus. In other words, the convention TV telephone apparatuses have been designed as non-portable so that, once the apparatuses are installed, it is hard to move them around and use them at any desired location.
The image quality of liquid crystal display (LCD) devices has been improved and are expected as a replacement of CRT. The use of the LCD device will contribute to a reduction of consumed power and will ensure compact and light TV telephone apparatuses. The telephone function may be designed separable from the TV telephone apparatuses so that those apparatuses become more compact and lighter. In addition, it is unreasonable that a person, if carrying an LC television that can show a dynamic image, is restricted to transmit only voices at time of using a telephone.
The conventional TV telephone apparatuses, even if designed compact and light, still require a troublesome connection of various input/output (I/O) terminals, a power terminal, etc. every time they are used as TV telephones. In particular, in a case that a TV telephone apparatus whose portability is important is likely to be carried out often, it is quite troublesome since the user should disconnect the I/O terminals, etc. when carrying the apparatus out, and should connect them again when using it. In addition, it is necessary to charge the battery of the TV telephone apparatus occasionally, and connect a full-charged or additional battery for a long time transmission/reception. This makes the conventional TV telephone apparatus further troublesome. As various I/O terminals, a power terminal, etc. should be connected upon every usage, persons who are not familiar with such connection will not easily make such connections. In other words, the conventional TV telephone apparatus is not user friendly.